How to Tell If a Diamond Is Real: 7 Home Tests (and 4 to Skip)

Your grandmother's ring turns up in a drawer. Or a ring from a holiday market still sparkles years later. Or you are about to pay serious money for a stone online. Sooner or later, almost everyone holds a sparkly stone up to the light and wonders: is this actually a diamond?

Quick answer: to tell if a diamond is real at home, start with the fog test, the flashlight test and a look through a 10x loupe, then check the metal stamp on the setting. A real diamond clears breath fog in a second or two, shows mostly white sparkle with flashes of colour, and usually has tiny natural marks inside. No home test is 100% sure, though. Moissanite fools most of them, and lab-grown diamonds are real diamonds, so only a jeweller's tester or a gem lab can give you the final word.

Below are the seven tests worth doing, the four to skip, and how to spot the most common look-alikes. We set diamonds by hand in Yerevan every week, so this is the same checklist we use ourselves.

Before you start: clean the stone

Almost every home test works better on a clean diamond. Diamonds attract oil, so hand cream and soap film make a real stone look dull and fog up for longer. Soak the piece for 15 minutes in warm water with a drop of washing-up liquid, brush gently behind the stone with a soft toothbrush, rinse and dry with a lint-free cloth. Now the stone is ready to show you what it is.

1. The diamond fog test

Hold the stone close to your mouth and breathe on it, the way you would fog up a mirror. Then watch the surface.

• A real diamond clears in about one or two seconds, because diamond spreads heat away very quickly.
• Glass and cubic zirconia (CZ) stay foggy for several seconds and clear slowly.

The diamond fog test is quick and free, but it has one big blind spot: moissanite also moves heat fast, so it clears quickly too. Treat a pass as "maybe", and a slow fog as a clear warning sign.

2. The flashlight test

This is the test people search for most: how to tell if a diamond is real with a flashlight. Go into a dim room, turn on your phone torch, and shine it straight down onto the top of the stone. Then tilt the stone slowly.

A real diamond sends back mostly bright white light (called brilliance) with short flashes of colour (called fire). Moissanite throws much stronger rainbow colours, like a tiny disco ball, especially in sunlight. CZ also shows lots of colour, while glass looks flat and a little watery.

It takes some practice, and the cut and the light change the result, so use it as a hint, not a verdict.

3. The read-through test (loose stones only)

If the diamond is loose, put it upside down (point up) on a line of newspaper print or a black dot on white paper. Look straight down through the stone.

A well-cut round diamond bends the light so strongly that you cannot read the letters or see the dot clearly. With glass or CZ, you can often make out the print or see the dot as a circle. This only works with round brilliant cuts that are not set in jewellery, so for a ring, move on to the next test.

4. Look through a 10x loupe

A jeweller's loupe costs a few euros and tells you more than any other home tool. Look at the stone from the top and from the side.

• Tiny marks inside: most natural diamonds have small crystals, feathers or dots, called inclusions. A stone that is perfectly flawless and cheap is suspicious, because CZ is usually flawless.
• Sharp facet edges: diamond is the hardest gem, so the edges between facets stay crisp. On glass and CZ they often look rounded or worn.
• Double lines: look in through the side of the stone. If the facet edges at the back look doubled, it is very likely moissanite, because moissanite splits light into two rays. A diamond does not.

5. The UV light test

Shine a UV (black) light on the stone in a dark room. Many diamonds glow, usually blue. This glow is called fluorescence, and roughly a quarter to a third of diamonds have it.

So what does a fake vs real diamond under UV light tell you? A blue glow is a good sign. No glow proves nothing, because most real diamonds do not glow at all. If every small stone in a ring glows exactly the same strong colour, that is worth a closer look by a jeweller.

6. Check the setting and the stamp

Jewellers rarely put a real diamond into cheap metal. Look inside the band or on the clasp for a stamp: 585 or 14K, 750 or 18K, or PT950 for platinum. A stamp that says "C.Z." means cubic zirconia. Green marks on the skin, worn plating or no stamp at all are red flags. Not sure about the metal itself? Our guide on how to tell if gold is real walks you through it.

Look at how the stone is held, too. Real diamonds sit in neat claws or a bezel, never in glue.

7. Use a diamond tester

A diamond tester is a pen-shaped tool with a metal tip. You touch the tip to the stone, and it beeps or lights up. There are two kinds, and the difference matters.

• A thermal tester measures how fast heat moves through the stone. It catches glass and CZ easily.
• A multi-tester also checks electrical conductivity, which it needs to catch moissanite.

So, does moissanite pass a diamond tester? On a thermal-only tester, yes, it usually reads as diamond. On a multi-tester, it shows up as moissanite. Most jewellers will test a stone for free in a minute, so this is the easiest final check before you buy or sell.

4 tests to skip

• The scratch test. Yes, diamond is the hardest natural material. But what can scratch a diamond? Only another diamond. And moissanite will scratch glass too, so the test proves nothing. Worse, a diamond can chip if you hit it at the wrong angle.
• The water drop test. A diamond sinks in a glass of water. So do CZ, moissanite and most glass, which makes this test useless.
• The heat and cold water test. Heating a stone and dropping it into cold water can crack a real diamond with inclusions. Never worth the risk.
• The bite test. Your teeth will lose, whatever the stone is.

Real diamond vs moissanite vs CZ vs glass

Here is how the common look-alikes behave in the tests above. On a phone, swipe the table sideways to see every column.

Moissanite vs diamond: the hardest one to spot

Moissanite is a lab-made gem, and it is the look-alike that fools people most. It is very hard, it clears fog quickly and it passes thermal testers. The giveaways are the stronger rainbow sparkle, the doubled facet lines under a loupe and the result on a multi-tester. Moissanite is a lovely stone in its own right. It just is not a diamond, and it should never be sold as one.

Are lab-created diamonds real?

Yes. Lab-grown diamonds are real diamonds: the same carbon, the same hardness, the same sparkle. They pass every home test and every standard diamond tester, because they are diamonds. The only difference is where they formed.

Can a jeweller tell if a diamond is lab grown? Not by eye, and not with a pocket tester. It takes lab equipment that reads how the crystal grew. That is why a grading report and a tiny laser number on the edge of the stone matter. The International Gemological Institute explains how labs tell lab-grown and natural diamonds apart.

The honest trade-off: lab-grown diamonds cost much less, but their resale value is low. Natural diamonds hold more of their value. Our diamond tennis bracelet comes in both options, natural or lab-grown, so you can choose with open eyes. We explain the difference in our honest guide to lab-grown vs natural.

When to see a jeweller

Home tests are good for a first answer. See a jeweller or a gem lab when:

• the stone passes your tests but you plan to insure, sell or inherit it,
• you need to know if it is natural or lab-grown,
• you are about to spend a lot on a stone without a grading report.

And if you are wondering where you can sell your diamond ring, get it tested first. A local jeweller with a multi-tester, or a report from a recognised lab, puts you in a much stronger position with any buyer.

Buying a diamond you never have to test

The easiest way to know your diamond is real is to buy from someone who will tell you exactly what it is. Every piece we make in Yerevan is described as it is. Our round solitaire engagement ring holds a natural 0.50 ct round brilliant diamond in 14K gold. Our princess cut engagement ring carries 0.75 ct of diamonds in total, and the hidden halo engagement ring hides a ring of diamonds under the centre stone. Still choosing? Read our simple guide to choosing an engagement ring.

We have been making jewellery since 2010, our gold is checked at the assay office, and if you want a stone set your way, ask us about custom gold jewelry.

Frequently asked questions

How do you know if a diamond is real at home?
Clean the stone, then try the fog test, the flashlight test and a 10x loupe, and check the metal stamp. If the stone passes all of them, ask a jeweller to confirm it with a multi-tester.

Does moissanite pass a diamond tester?
On a thermal-only diamond tester, moissanite usually passes as diamond. A multi-tester, which also checks electrical conductivity, shows it as moissanite.

Can you scratch a diamond?
Only another diamond can scratch a diamond. But a hard knock at the wrong angle can chip it, so never use a scratch test at home.

Do real diamonds glow under UV light?
Some do. Roughly a quarter to a third of diamonds glow, usually blue. Most do not glow at all, so no glow does not mean the stone is fake.

Are lab-grown diamonds fake?
No. Lab-grown diamonds are real diamonds with the same chemistry and hardness as natural ones. They are cheaper to buy, but they have a much lower resale value.

Back to the ring in the drawer

So, grandmother's ring. Breathe on it, shine a light on it, look closely. If it clears fast, sparkles mostly white and shows a tiny mark or two under the loupe, there is a good chance it is the real thing. Take it to a jeweller for the final beep, and then wear it. A diamond is meant to be worn, not kept in a drawer.

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Handmade in Yerevan since 2010 · 14K gold · real diamonds